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	TABLE OF CONTENTS Home Home WiNet Is WiMedia ready?

Bluetooth
Just as USB is associated with the PC, Bluetooth is associated with mobile phones. Last summer the billionth Bluetooth chip shipped. The Bluetooth SIG has adopted WiMedia as the basis for Bluetooth 3.0. Technical details of the implementation have not been released by the Bluetooth SIG working group, but the study group which recommended adopting WiMedia publicly announced some guidelines.

Bluetooth 3.0 will be backwards compatible with earlier versions of Bluetooth. This means there will be two radios side by side or two radios built into the same chip or module. Staccato Communications demonstrated a USB Mini Card Slot device that includes Staccato's Ripcord single-chip CMOS WiMedia radio sharing an antenna with a Bluetooth device. Because the UWB radio and Bluetooth radio don't interfere with one another, both radios can operate simultaneously using the same antenna.

Figure 1: WiMedia Bluetooth Mini Card -- Two radios share single antenna

WiMedia and Bluetooth are complementary from a power usage perspective. WiMedia is the most power efficient means for moving bits in terms of joules per bit . WiMedia achieves this efficiency because its high transfer rate allows it to transmit many bits in a short period of time. On the other hand Bluetooth is more efficient at keeping a link open as it is able to wake up every few seconds, send a short message and go back to sleep.

The Bluetooth SIG expects to use conventional Bluetooth in its standby mode keeping the WiMedia radio completely off until such time as it is needed to transfer a file or stream video or audio.

Today Bluetooth has a significant advantage over WiMedia in standby or sleep modes in that it is a simpler radio and can be implemented in a fewer number of transistors. Bluetooth in its standby modes consumes only a few micro watts of power.

There are two techniques of achieving low power states for digital circuitry, clock gating and power gating. With clock gating, you turn off the clock driving the circuitry, and current usage drops, but there is still leakage. When there are millions of transistors, leakage becomes significant. With power gating, you turn off power to selected sections of the chip, and no current is used.

Chip designers believe the 'low transistor count' advantage of Bluetooth's simpler radio will disappear as power gating techniques become more sophisticated. Today the latest generation Wi-Fi chips designed for portable devices match Bluetooth power consumption in low power modes. First generation WiMedia draws more power than Bluetooth in low-power modes, but chip designers believe that over time this differential will diminish as power gating is deployed in next generation WiMedia chips.

For mobile phone applications, power gating is combined with a slower clock to enable standby modes where power is measured in micro watts. Normally WiMedia chips operate at a clock speed of 528 MHz, but mobile phones operate low power devices at 32 KHz. In sleep mode most of the chip is turned off through power gating, but a count down timer and just enough circuitry to restart the chip remains powered and runs on the 32 KHz clock. In this mode the system draws very little power.

In any case WiMedia based Bluetooth 3.0 radios will meet the demands for low cost, high throughput and low power consumption demanded by the mobile phone industry.

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